The present invention relates to digital to analog conversion apparatus and more particularly to pulsewidth modulated, charge transfer digital to analog conversion apparatus. U.S. Pat. No. 3,646,545 discloses a charge-gated digital to analog converter. The digital input signal is provided to an analog signal generating circuit, including a counter, which on command, generates an analog signal in the form of a pulsewidth which is a representation of the magnitude of the digital input signal and is a proportion of a predetermined maximum pulsewidth. U.S. Pat. No. 3,707,713 shows a high resolution pulse rate modulated digital to analog conversion system wherein means are provided for generating intermediate encoded digital signals which are a function of the binary digital data located in stored digital intelligence means. Monolithic digital to analog converters in this application require holding registers and output amplifiers. The resultant space utilization with these components is very inefficient. Pulsewidth modulated digital to analog converters satisfy the performance requirements when operated in a continuous duty update mode but have extremely long time constants when operated in a sample data mode (as required in a conventional computer interface).
The present invention is an improvement over the prior art such as U.S. Pat. No. 3,646,545 which eliminates the need for a register and output amplifiers.